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From everything I have read, you probably used non-stick aluminum foil which has a light teflon coating. The coating melts and ahderes to the oven surface at temperatures 350F and greater.
Many people have had the same problem. The closest to a solution I could find was in a forum where the user says...

"I did the same thing last night and freaked because the oven is only about a month old. I called Sears and this is what they said to do:

BE CAREFUL, remove as much of the foil as possible Turn oven on to 200 lay an old wet bath towel on top Use a plastic spatular to remove the foil

They said it will take sometime to remove the foil, in some casesdays, and that you can still use the oven but DO NOT use the selfcleaning untill all the foil is removed."

Unfortunately, several people reported they were never able to remove the foil. Best of luck.

pull off as much of the foil as you can and then spray the fringes of it with some oven off oven cleaner. Use rubber gloves as this is a strong chemical. Let it sit for thirty minutes and then pull off as much more foil as possible. Repeat until the bottom of the oven is clean.

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Unfortunately you can't remove that foil, you will end up doing more damage to the liner. the only thing you can do is replace the liner. And it's a big job, if the manufacture makes a replacment part for your unit, and if they do it will be costly.
Good luck....